1. Field of the Invention
The present invention relates to a brushless rotary electric machine and, particularly, a field-coil type rotary electric machine having permanent magnets to be directly connected to an engine.
2. Description of the Related Art
A common field-coil type AC generator (or alternator) that has a rotor with a plurality of claw poles and a field coil, brushes and slip rings has two air gaps in a magnetic circuit, while a brushless field-coil type AC generator has four air gaps in a magnetic circuit. Although such a brushless rotary electric machine is excellent at operation without maintenance work, it can not generate as much output power as a common rotary electric machine having brushes and slip rings because of more air gaps. A plurality of permanent magnets can be substituted for the field coil to reduce the number of air gaps. However, it is difficult to control the magnetic flux supplied to the armature winding or the output voltage thereof.